The interest of our laboratory is the determination of the physiological basis for the minimum temperature of growth. The primary objective of this proposal is the determination of the biochemical and/or physical basis for bacteriophage dependent minimum and maximum growth temperatures. For this we are studying the physiology of psychrophilic phage infected Pseudomonas species. These studies are being conducted at temperatures permissive to host growth but nonpermissive to phage production and at temperatures nonpermissive to host growth but permissive to phage production. We are presently studying changes in the proteins associated with permissive infections and partially absent from nonpermissive infections.